The research being carried out under this project is directed at metabolic studies of total parenteral nutrition (TPN) in infants. Specifically, the following areas are being studied: (a) definition of optimal protein requirement in the content of TPN over a range of 2.0 to 3.0 g/kg/d, (b) identification of abnormalities of plasma amino acids produced by various intravenous amino acid preparations with the specific purpose of constructing dose-response curves for urinary excretion of single amino acids will also be investigated, (c) studies of the metabolic fate of N15 urea and N15 arginine in infants receiving TPN in order to compute the degree of recycling of urea as well as to compute net protein synthesis, (d) study of the essential fatty acid patterns in plasma of infants receiving conventional fat-free TPN infusates as well as the effects of intravenous fat emulsions upon such patterns, and (e) study of plasma and urinary RNase as measures of recovery from malnutrition in infants being nourished by TPN.